Seleno anions

Tin forms soluble thio(seleno)anions. The sulphides tend to be soluble in very alkaline solutions. 

A similar principle is observed in the reaction of seleno-anions 88 with ketones and aldehydes Eq. 

Other Thio- and Seleno-Oxocompounds with Anions of Cs or C2v Symmetry 94... 

On-line anion exchange LC/ICP-MS methods for selenium and chromium speciation have been published [30], In studies of selenium speciation in environmental samples LC/ICP-MS and LC/ ESI-MS methods have been used for the determination of both inorganic and organic selenium species [43]. For the determination of methyl selenide, strong anion exchange and RP chromatography have been employed [43], while for the determination of seleno-aminoacids, IP RP chromatography with on-line detection based on ICP-MS has been successfully employed [44],... 

S. Cavalli, N. Cardellicchio, Direct determination of seleno-amino acids in biological tissues by anion-exchange separation and electrochemical detection, J. Chromatogr. A, 706 (1995), 429-436. 

SEC and anionic HPLC-Q-ICP-MS can be used to determine the approximate molecular weight of Se-containing proteins and identify fractions for seleno-amino acid analysis. The coupling of anion and cation HPLC and Q-ICP-MS also allows selenoamino acids in hydrolyzed protein extracts to be measured. However, the lack of knowledge about species, low Se concentrations, and lack of detection power make quantification of Se species difficult. The concurrent use of HPLC-MS-MS is needed to confirm the identity of Se species, but at present the low concentrations of Se in extracts preclude its use. It is essential that CRMs are used to confirm the validity of results regarding total Se and Se species. 

The selenide anion can be used in the heterocyclization of polyhydroxylated selenepane 122 and 124 starting from l,2 5,6-dianhydro-3,4-0-methylidene-L-iditol 121 or from D-mannitol 123 in variable yield (Scheme 10). A general, known method is to combine an acylation for purification and deacetylation by methanolysis but Le Merrer el al. simplified this procedure to obtain directly the crystalline selenepane after flash chromatography. Deprotection of these seleno compounds gave an inextractable mixture <1997T16731>. 

Selenenyl halides are relatively stable, though moisture sensitive, compounds that are generally prepared by the reactions shown in Scheme 7 and behave as electrophihc selenium species. " They react with ketones and aldehydes via their enols or enolates to afford a-seleno derivatives (e.g. (17) in equation 11). Similar a-selenenylations of /3-dicarbonyl compounds, esters, and lactones can be performed, although the latter two types of compounds require prior formation of their enolates. Moreover, the a-selenenylation of anions stabilized by nitrile, nifro, sulfone, or various types of phosphorus substituents has also been reported (equation 12). In many such cases, the selenenylation step is followed by oxidation to the selenoxide and spontaneous syn elimination to provide a convenient method for the preparation of the corresponding a ,/3-unsaturated compound (e.g. 18 in equation 11). Enones react with benzeneselenenyl chloride (PhSeCl) and pyridine to afford a-phenylselenoenones (equation 13). 

Table XLI summarizes the structures of known, homogeneous, anionic selenocyanate complexes. Although fewer examples exist than for the corresponding thiocyanate complexes, it is apparent that a similar pattern exists for the two sets of complexes. Class a metals are coordinated by the nitrogen atom, whereas selenium is the donor for the class b metals. In mixed metal complexes containing bridging seleno-oyanate groups the nitrogen atom coordinates to the harder or class a metal, and the selenium atom bonds to the softer or class b metal, as was observed with the corresponding thiocyanate complexes.

The treatment of vinyl anions with elemental selenium also leads to seleno-carbonyl compounds via eneselenolate anions (Eqs. 4-6). Deprotonation of l,3-selenothio-2-thione with EDA followed by the reaction with elemental selenium proceeds accompanied with the rearrangement of vinylic skeleton to form l,3-dithio-2-selone derivatives (Eq. 4) [38]. The vinyl anions from oxa-zolines and imidazoles were treated with elemental selenium to give the oxazo-line selone and imidazoline selone after the aqueous workup (Eq. 5) [39]. The reaction of vinyl magnesium halides with elemental selenium and allyl bromide gives allyl vinyl selenides that undergo a seleno-Claisen rearrangement to generate y,6-unsaturated selenoaldehydes (Eq. 6) [40]. 

Addition of phenylethynethiolate or -selenate to the carbene complex 185 (M = Cr or W, R = Me or Et, E = S or Se) affords an anionic adduct (186) which, unexpectedly, contains a reactive thioketene function. Electrophiles can attack either at the sulfur or at the carbon a thereto to produce coordinated carbenes or thio- and seleno aldehydes and esters [H4J45). 

Scheme 74), by selenenylation of a-selenoalkyl anions (Scheme 75) - and by alkylation of 1,1-bis(seleno)alkyl metals (Schemes 26,76 and 77).iW5j6,7i,73,ioo,i04... 

Bis(seleno)alhfl metals as acyl anion equivalents... 

S2.1 I,l-Bis(seleno)alkyl metals as acyl anion equivalents 2.6.522 1,1-Sllyl-l -selenoalkyl metals as acyl anion equivalents 2.6 J3 Homologation of Carbonyl Compounds from a-Heterosubstituted-ai-selenoalkyl Metals 2.6J.4 Conclusion... 

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